1. Field of the Invention
The present invention relates to a semiconductor device, which has a structure that includes an epitaxial layer buried in trenches formed in a semiconductor layer, and method of fabricating the same.
2. Description of the Related Art
In recent years, an SJ (Super Junction)-MOSFET has been known as one of low-loss power semiconductor devices. The SJ-MOSFET has a superjunction structure in a drift layer as a structure that satisfies a low on-resistance and a high breakdown voltage of a power MOSFET at the same time. In the SJ-MOSFET, trenches are formed in an n-type epitaxial layer periodically along the plane, and a p-type epitaxial layer is formed in these trenches. To form such the periodic structure, an n-type drift layer is formed on an n-type substrate by epitaxial growth, and deep trenches are formed in the n-type drift layer by an isotropic etching. Next, a p-type resurf layer is formed in the trenches by epitaxial growth. Then, the surface is planarized by CMP (Chemical Mechanical Polishing) to expose the n-type drift layer to the surface (JP-A 2003-124464, paragraphs 0047-0048, FIGS. 2-5).
As fine pattering of the element proceeds and the aspect ratio of the trench increases, the growth speed of silicon at the time of epitaxial growth may become slower at the interior of the trench than at the entry to the trench. In this case, a void may arise inside the p-type resurf layer buried in the trenches. When such the void is exposed to the surface of the semiconductor layer in the planarization step by CPM and results in a problem associated with mixture of dusts into the void, a problem arises because the delivery to the post step can not be achieved.